I think by "mouth breathers" they mean folks who are willing to dehumanise folks less lucky than themselves to have been born somewhere with relative economic prosperity because this is "our country".

Also, those same people who are willing to buy newspapers that _gleefully_ employ columnists who also dehumanise these humans on an almost daily basis.

People who fall for populist nonsense just before an election spouted from a government who have, over more than a decade, entirely failed to reduce immigration and yet convince the electorate that they're the best people for that particular job.

I also reject the notion that the majority of the population would like immigration reduced (I certainly don't, especially refugees fleeing wars that we are at least, in part, responsible for). Considering the chronic shortage of skilled workers in the UK (due to our underfunded education system), I don't see how that's possible.